This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Understanding such fundamental cell biological processes as migration, polarization and cell division requires the ability to noninvasively observe the dynamic changes in the structure of the involved subcellular compartments. Routinely used modes of observing these processes often require invasive imaging methods that rely on the introduction of dyes or toxins or fixation. In turn, introduction of these compounds can yield artifacts as well as impede sequential imaging. This study proposes to use an integrated multiphoton microscopy and optical coherence tomography (MPM/OCT) system as a means of observing subcellular compartments without the application of exogenous sources of contrast. The previous development of an MPM/OCT platform has permitted simultaneous observation of co-registered fluorescence and scattering contrast in cells and tissues. High contrast of scattering in the OCT modality has shown clear structures which are like actin filopodia. Both auto-fluorescence and scattering are intrinsic contrasts in cells and tissues. Furthermore, MPM/OCT can provide high-resolution and 3-dimensional images, which means cells can be observed in their natural environment of 3-dimensional extracellular matrix. Data from the proposed experiments will specifically characterize the biological basis of those structures that provide OCT contrast. It may provide the basis for a novel method of studying cytoskeletal or membranous dynamics in unlabelled cells in a more natural 3-dimensioal environment.